Method of producing shaped bodies of regenerated cellulose from viscose and spinning solution and bath therefor



United States Patent 3,112,158 METHOD 0F PRGDUCTNG SHAPED BODIES 0F REGENERATED CELLULOSE FROM VESCUSE SPENNHNG SQLUTIUN AND BATH THERE- Richard H. Eraunlieh, West Chester, and Theodore S.

Matter, Upper Darby, Pa, assignors, by mesne assignments, to FMC Corporation, San Jose, Calif., a corporation of Deiaware No Drawing. Filed July 2, 1959, Ser. No. 824,478 Claims. (Cl. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated celluloss from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing Zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of vdemarkation between the two. The

cross-section of the filaments exhibits a very irregular or ent in the spinning bath. The skin and core portions of F the filament represent diiferences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flexlife, is subjected to fibrillation and is relatively stiff.

One of the important uses of viscose rayon filaments is in the reinforcement of molded rubber products, such as automobile and like tire casings. For such purposes, the strength of the filaments is one of the primary considerations. It is known that, in general, the greater the uniformity of the structure of the cellulose in the filament, the higher the tenacity or tensile strength. It is known that by increasing the proportion of skin in the filament, improvements result and present day filaments, such as utilized as pneumatic tire casings, generally consist of at least about 75% skin. It is also known that in twisting of viscose rayon filaments, an appreciable loss in tensile strength occurs, that is, the tensile strength or tenacity of a twisted bundle of filaments is lower than the sum of the tenacities of the individual untwisted filaments. In the forming of tire cord, for example, a bundle of filaments is twisted in one direction and the cord subsequently formed from a plurality of such twisted bundles, the twisted bundles being twisted in the opposite direction when they are plied into the cord. :Because of the loss of strength in twisting, a very small improvement in the tenacity of the individual filaments is of utmost importance so as to obtain appreciable improvements in the tensile strength or tenacity of the final cord.

It has been discovered that appreciable improvements in cord strength may be effected by spinning viscose into a low acid-high zinc spinning bath in the presence of glyoxal. The glyoxal may be added to the viscose batch, or it may be injected into the stream of viscose just prior to extrusion of the viscose through the spinneret or the glyoxal may be present in the spinning bath. The viscose may contain coagulation modifiers which are known to the art, their principal purpose being to produce smoothsurfaced products consisting of a large proportion of skin.

The viscose may contain from about 4 percent to about 10 percent cellulose, the particular source of the cellulose being selected for the utimate use of the regenerated cellulose product. The caustic soda content may be from about 4 percent to about 11 percent and the carbon disulfide content may be from about 32 percent to about 60 percent, preferably between 35% and 50%, based upon the weight of the cellulose. The viscose should have a salt test number or index above about 6 and preferably about 10 or higher at the time of spinning or extrusion. The salt test is an indication of both the amount of carbon disulfide added to the viscose and the degree of aging. The salt test number is the minimum percent concentration of sodium chloride solution at 18 C. required to coagulate 3 drops of viscose. It is determined by dropping the viscose into a beaker containing about 40 cc. of sodium chloride solution at 18 C. while stirring. Stirring is continued for 90 seconds after the last drop of viscose has been added.

Generically and in terms of the industrial art, the spinning bath used in the practice of the present invention is a low acid-high Zinc spinning bath. The bath should contain from about 10' percent to about 25 percent sodium H sulfate and from about 4 percent toabout 15 percent zinc sulfate, preferably from 15 percent to 22. percent sodium sulfate and from 5 to 12 percent zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., though at the lower temperatures the higher concentrations of sodium sulfate cannot be used because of the difficulty of solubility. However, at the preferred temperatures of between about 45 C. to about C. solubility is no problem. The temperature of the spinning bath is not critical. However, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength are affected by the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 45 C. and 75 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. The acid content of the spinning bath should preferably not exceed about 9 to 10 percent while the zinc sulfate should preferably be within the range of 5 percent to 12 percent. It has been found that higher acid contents can be used and still exceptionally high-skin, high-tenacity yarns obtained if the carbon disulfide content of the viscose is increased and the zinc sulfate content of the bath maintained at a reasonable high level such as above 8.0 percent. Thus, even through in practicing the present invention it is generally preferred that the acid concentration of the hath not exceed about 9 percent, satisfactory products having the desired high proportion of skin and high-tenacity will be obtained at higher acid concentrations up to as high as 11 percent if the carbon disulfide content of the viscose is sulficiently increased and the zinc sulfate of the spinning bath is not appreciably below 8.0 percent.

Though various terminology may be used to indicate the point at which the viscose is sufiiciently coagulated to permit uniform withdrawal from the spinnere-t, for purposes of the present application, the term slubbing point will be used. This lower acid concentration is readily determined by those skilled in the art through observance of the fibers as formed and has no particular effect on the production of high-skin, high-tenacity products in practicing the present invention. It is apparent that as the canstic soda content of the viscose is increased, a higher acid concentration is required due to the partial neutralizing effect of the increased caustic soda.

In the producton of filaments for such purposes as the fabrication of tire cord, the filaments are stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70 percent to about 175 percent, preferably between 125 percent and 150 percent. Yarns for other textile purposes may be stretched as low as percent. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns for tire cord purposes but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1 percent to about 5 percent sulfuric acid and from about 1 percent to about 5 percent sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared as herein described have a smooth or non-crenulated surface and consist of at least about 75% skin. Filaments produced pursuant to this invention have a high toughness and a greater flexing life which may be attributed by the greater uniformity in structure throughout the filament.

As pointed out hereinbefore, in the twisting of bundles of filaments and the plying of such twisted bundles to form conventional cords as utilized in reinforcing molded rubber articles, there is a loss in strength. Generally, in considering the suitability of filaments and fibers for the production of this type of reinforcing cord, reference is made to the percent conversion factor. The percent conversion is determined by dividing the strength of the cord, that is, the tension at the breaking point by the total strength of the untwisted filaments which form the cord and multiplying by one hundred. Present day commercially available tire cord rayon is said to have an average percent conversion of about 85%, that is, a cord formed from rayon filaments has a tensile strength of approximately of the tensile strength of the combined untwisted filaments in the cord. There is an appreciably less loss in tensile strength in the production of twisted cords from filaments prepared in accordance with the present invention as compared to the loss in tensile strength of conventional textile grade and tire cord grade rayon filaments. "In the examples which follow, bundles of filaments having a denier of about 1120 to 1130 and containing about 980 filaments were twisted fourteen turns per inch. Two such twisted bundles were then piled together by twisting fourteen turns per inch in the opposite direction. The tension required to break the bundle of untwisted filaments was determined and the breaking strength of the cord identified as a 14 x 14Y cord was also determined. The percent conversion was then calculated by dividing the breaking strength of the cord by twice the breaking strength of the bundle of untwisted filaments and multiplying by one hundred. In general, cords formed of filaments as made by the present invention have a percent conversion of from about to about 96%.

The amount of glyoxal employed is dependent upon whether it is incorporated in the viscose or in the spinning bath. Amounts of from about 0.5% to about 4% based on the weight of the cellulose in the viscose are satisfactory when the glyoxal is added to the viscose either to the entire batch or where it is injected into the stream of viscose just prior to extruding the viscose through the spinneret. Where the glyoxal is incorporated in the spinning bath, the amount present in the spinning bath does not appear to be critical. The amount may be as low as about 0.005% and may vary up to 1% and more based on the weight of the spinning bath. Because of the economics involved, large proportions merely add to the cost of the product without effecting corresponding improvements in the product. In general, it is prefer'redto employ amounts of from about 0.005% to about 0.1%-

As also pointed out hereinbefore, it is preferred to in-' corporate in the viscose a substance or a combination of substances which are well known in the art and are commonly designated as coagulation modifiers. In general, these substances, when incorporated in the viscose, result in products consisting of a large proportion of skin or substantially entirely of skin and the products have smooth, non-crenulated, exterior surfaces. Specific examples of some of these substances are set forth in the following patents: 2,535,044; 2,536,014; 2,696,423; 2,792,278; 2,792,279; 2,792,280; 2,792,281; 2,840,448;

2,895,788; 2,898,182 and French Patent 1,162,737. Sim.- ilarly, bath additives may be incorporated in the spinning bath to improve spinning conditions such as reduction in spinneret incrustation.

In general, these coagulation modifiers are incorporated in the viscose in amounts of from about 0.25% to about 4% depending upon the specific coagulation modifier. When combinations of two or more modifiers are incorporated in the viscose, they are present in amounts of at least about 0.25% of each modifier and the t a amount of modifier generally does not exceed about 4%. Excess amounts appear to decrease the tensile strength of the filaments. It has been found that similar limits hold when glyoxal is incoporated in the viscose or is present in the spinning bath. For example, the viscose may contain about 1.5% glyoxal and 1.5% of a known coagulation modifier, the percentage being based on the weight of the cellulose in the viscose. Alternatively, the viscose may contain 1.5% of each of two coagulation modifiers. In the examples which are set forth hereinbelow, specific known coagulation modifiers have been included merely for purposes of illustration.

The invention may be illustrated specifically by ref erence to the preparation of regenerated cellulose filaments from a viscose containing 7.5% cellulose, 6.5% caustic soda, and having a total carbon disulfide content of about 40% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 40% carbon disulfide, based on the weight of the cellulose, and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The viscose was then allowed to ripen for about 20 hours at 18 C.

Yarns or bundles of filaments were formed by extruding viscose through a spinneret to form a yarn of about a 1100 denier containing about 980 filaments. The viscose had a sodium chloride salt test of about to 10.5. The aqueous spinning baths contained 7.2% sulfuric acid, sodium sulfate and 7% Zinc sulfate and were maintained at a temperature of about 65 C. After removal of the filaments from the spinning baths, they were passed through a hot aqueous bath containing about 4% sulfuric acid maintained at a temperature of about 90 C. During the travel of the filaments through this hot bath, they were stretched about 130% to 150%.

In the examples reported in Table I, additions of substances were made to the viscose and the percentage of the substances is reported on the basis of the weight of the cellulose in the viscose. The substance identified as DCO is a coagulation modifier as disclosed in the copending application of Byron A. Thumm, Serial No. 628,499, filed December 17, 1956, now Patent No. 2,962,342, and consists of ethers formed by reacting castor oil and ethylene oxide, the mixture of ethers containing an average of 81 ethylene oxide units per molecule of castor oil. The data included under the heading Singles are the tenacity, in grams per denier, and elongation of the untwisted filaments. The data included under the heading Cord is the breaking strength, in pounds, and the elongation of a 14 x 14Y cord formed as above described.

Table 1 Singles Cord Added Substance Tenacity, Percent Breaking Percent gin/d. Elongation Strfingth, Elongation The individual filaments have a smooth, non-crenulated surface and consist largely of skin; that is, at least to skin. Although a viscose of a specific composition was used in the foregoing examples, any desired viscose is satisfactory and the improvements described are obtained regardless of the specific composition.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60 percent and 30 percent alcohol for a few moments each, and it is then stained in 2 percent aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10 percent water and 90 percent dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. A viscose spinning solution to which has been added from about 0.5% to about 4%, based on the weight of the cellulose in the viscose, of glyoxal.

2. A viscose spinning solution containing a coagulation modifier and to which has been added from about 0.5% to about 4%, based on the weight of the cellulose in the viscose, of glyoxal.

3. An aqueous spinning bath for the production of regenerated cellulose products from viscose containing from about 10% to 25% sodium sulfate, from about 4% to 15% zinc sulfate, up to about 11% sulfuric acid and from about 0.005% to about 1% glyoxal.

4. In a method of producing shaped bodies of regenerated cellulose from viscose, the step which comprises extruding viscose having a sodium chloride salt test of at least about 6 into an aqueous spinning bath in the presence of glyoxal.

5. The step in the method as defined in claim 4 wherein the viscose contains from about 0.5 to about 4%, based on the weight of the cellulose in the viscose, of glyoxal.

6. The step in the method as defined in claim 4 wherein tne spinning bath contains from about 0.005% to about 1% glyoxal.

7. In a method of producing shaped bodies of regenerated cellulose from viscose, the steps of adding to and incorporating in viscose from about 0.5 to about 4%, based on the weight of the cellulose in the viscose, of glyoxal and extruding the viscose at a sodium chloride salt test of at least about 6 into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from 1 Stretch for this example,

Stretch much higher ruptures filaments.

- Spinning bath contained 15% sodium sulfate, 7% zinc sulfate and 5.5% sulfuric acid.

about 4% to 15% zinc sulfate and up to about 11% sulfuric acid.

8. In a method of producing shaped bodies of regenerated cellulose from viscose, the steps of preparing an aqueous spinning bath containing from about 10% to 25 sodium sulfate, from about 4% to 15% zinc sulfate, up to about 11% sulfuric acid and from about 0.005% to about 1% glyoxal and extruding into the spinning bath viscose having a salt test of at least about 6.

9. In a method of producing shaped bodies of regenerated cellulose from viscose, the steps of adding to and incorporating in viscose from about 0.5% to about 4%, based on the weight of the cellulose in the viscose, of combined dirnethylarnine and polyethylene glycol and extruding the viscose at a salt test of at least about 6 in the presence of glyoxal into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 4% to 15% zinc sul ate and up to about 11% sulfuric acid.

10. The steps in the method as defined in claim 9 wherein the spinning bath contains from about 0.005%

to about 1% glyoxal.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,583 Jackson et a1. July 20, 1943 2,346,759 Jackson et al. Apr. 18, 1944 2,516,113 Gray July 25, 1950 2,535,045 Cox Dec. 26, 1950 2,792,313 Charles et al. May 14-, 1957 2,853,360 Thumm Sept. 23, 1958 2,942,931 Mitchell June 28, 1960 FOREIGN PATENTS 812,254 Great Britain Apr. 22, 1959 

4. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE FROM VISCOSE, THE STEP WHICH COMPRISES EXTRUDING VISCOSE HAVING A SODIUM CHLORIDE SALT TEST OF AT LEAST ABOUT 6 INTO AN AQUEOUS SPINNING BATH IN THE PRESSENCE OF GLYOXAL. 